Why Is MLS Different?

I’m not going to offer a purported answer now, I’m just asking questions, specifically: Why is real estate immune from the ideas being debated in other industries? Doc Searls wrote some time ago:

To really take advantage of open source, he explained, you need to value ubiquity in your marketplace at least as much as you value scarcity in your product portfolio. In fact, your smartest move may be to take some of the products you’re selling, and make them ubiquitous by moving them from proprietary/closed to open/public domain â€” literally, from scarcity to ubiquity:

Open Social paves a way to a potentially new kind of web culture. In that culture, companies would recognize that users are entitled to their information. It should be importable and exportable. It should not be locked in.

Why is real estate sales through the MLS excepted from this general idea? I’m not asking this rhetorically, I honestly don’t know and wonder about the answer. Interestingly enough, the idea that data should not be locked in applies just as much to companies like Zillow as it does to MLSs, maybe more so. So, what do you think is the answer? Where is MLS data on the curve towards ubiquity and commoditization?